Various techniques have been proposed for the separation of carbon dioxide from gas mixtures. For example, Winnick, J., Marshall, R., and Schubert, F., “An Electrochemical Device for Carbon Dioxide Concentration. I. System Design and Performance,” Ind. Eng. Chem., Process Des. Develop., Vol. 13, No. 1, 1974, pp. 59-62 describes the use of electrochemical cells for carbon dioxide concentration. These and similar methods use electrochemical or “polarization membranes.” These membranes operate on the principle that CO2 is converted to soluble carbonates at high pH and is liberated again at low pH. A pH gradient is constructed across a semi-permeable membrane. CO2 is preferentially absorbed on the basic side and released on the acidic side.
U.S. Pat. No. 6,579,343 describes techniques for purifying gas by contacting the gas with a liquid ionic compound. Natural gas may be purified, removing water and carbon dioxide.
U.S. Patent Application Publication No. 2007/0119302 describes polymeric materials containing ionic groups, which can be used as membranes and sorbents for separating gas components, such as CO2 from flue gas and natural gas. A polymer can have a polymeric backbone and ionic liquid moieties attached to the backbone.
It would be advantageous to have improved techniques for using ionic liquids such as in separating gases.